The present invention relates to an ignition system for internal combustion engines with high-tension switches.
More particularly, it relates to an ignition system in which at least one trigger diode cascade, as high-voltage semiconductor switch, is connected in a secondary circuit of each ignition coil prior to each spark plug and changes suddenly from a blocking state to a conducting state at a preselected voltage for generating ignition sparks.
The ignition system mentioned above uses high-voltage switches which are arranged on the secondary side, preferably in the spark plug terminal. Trigger diode cascades are used as high-voltage switching elements. A stack of 10 to 50 trigger diodes is used depending on the electric strength of an individual trigger diode and depending on the desired breakover voltage. With such a high-voltage semiconductor switch which changes suddenly from the blocking state to the conducting state, it is possible practically to eliminate the influences of shunts at the spark plug. Because of their self-capacitance, long ignition lines subsequent to the trigger diode cascade negatively affect the steepening effect of the trigger diode cascade. For this reason, the high-voltage semiconductor switch is preferably arranged in the spark plug terminal. In contrast, relatively long lines prior to the trigger diode cascade have an advantageous influence because, due to their self-capacitance, they suddenly release the stored energy as the high-voltage semiconductor switch becomes conductive. When such semiconductor switching elements are used in double ignition coils, the division of voltage on the secondary side makes it necessary to keep the breakover voltage of the high-voltage semiconductor switches low enough so that this breakover voltage is achieved in every case. However, this has the disadvantage that there is hardly any steepening effect when the breakover voltage is clearly below 11 kV.